This study proposes to: characterize ADPKD patients at greatest risk for progression to end stage renal disease (ESRD) in a prospective fashion, determine if magnetic resonance imaging (MRI) as opposed to ultrasound is more reliable and accurate in measuring renal volume and the change in renal volume over time in ADPKD patients, determine if progression of renal disease in high risk ADPKD subjects followed early in the course of their disease is better detected by change in renal volume as opposed to change in glomerular filtration rate, determine if specific mutations in the PKD1 or PKD2 gene are associated with more aggressive phenotype.